[Doc-t]

The idea that both you and your veterinarian “suspect IR (insulin resistance)” is evidence to me that he is IR. In fact, about 50% of all humans in the US have IR even if they show no outward signs and about 100% of obese people are IR. For horses this means if they have excess body fat (fat pads, crested neck) and look “metabolic” then they are IR.

What does IR have to do with your horse reacting to SBM (soybean meal)? I believe this is due to the protein (the amino acids of the protein) becoming sugar through gluconeogenesis instead of becoming muscle and other protein based structures in your horse.

In humans, it has been discovered that when there is IR, protein is converted into glucose (sugar / carbs). The reasoning is because the brain needs glucose moment by moment but insulin takes excess glucose and converts it into triglycerides (body and liver fat). In essence, when glucose intake is in excess of needs the brain is starved of glucose. Converting protein into glucose is a survival mechanism.

If your horse is being fed glucose in excess of his needs then insulin will be high and therefore resisted. The excess glucose comes from the starch (the plant version of glucose storage) of pasture and hay. If a horse has unrestricted access to pasture and / or unrestricted access to hay then he is consuming glucose in excess. Add to this any high quality protein such as SBM or good quality protein such as alfalfa and the glucose in the body goes up.

In humans and horses, there is an alter-ego hormone to insulin called glucagon. I write about this in my blog here. Go to the section called “So when do I stop feeding SBM?” When there is more insulin than glucagon (in other words, when the insulin to glucagon ratio is more than 1:1, or I:G >1) the body will be unable to convert body fat into fuel for the cells. In America eating the standard diet, the I:G is 4:1. This is leading us into an obese nation. If a high protein diet is added to the standard diet (for instance eating a large steak plus the bread and dessert) then the I:G goes to 70:1. In other words there is an insulin spike and the steak is mostly turned into sugar.

However, when the glucose intake is restricted so the I:G is 0.8:1 then adding the same amount of protein causes no spike in insulin. The protein is then converted into structural protein. A side note – using the “Protein Leverage Hypothesis,” when amino acid intake meets the daily needs, hunger is diminished (satiated). A good indicator of your horse not receiving enough protein even when being fed SBM would be an insatiable appetite as well as little to no fat loss and no improvement in hair coat, hoof condition or top line. And all of these indicators are usually poor in horses with equine metabolic syndrome (EMS).

Limiting consumption of all forage by restricting eating times of all forage to 12 hours, turning out on a dirt lot or reducing or soaking in water the hay are all avenues to glucose reduction. Clients who have restricted eating for 12 hours (for example from 6 pm to 6 am) have found their horses to become more comfortable. Not only are you reducing the glucose intake but you are allowing hormesis.

But in addition to glucose restriction, there is another factor. It is insulin independent glucose uptake into cells. This is a “back door” way to consume glucose that will not cause an increase in insulin. This pathway occurs when aerobic exercise is added consistently. Remember the adage “diet and exercise?” It turns out that we know know about this alternate pathway to glucose disposal. If you horse is not suffering from laminitis, then increase their exercise. In humans, aerobic exercise is achieved when the maximum heart rate (HR) equals 180 minus your age. I’m not sure what it is in horses but I know that if the only exercise for your horse is walking out to the pasture then he is not aerobically exercising.

In summary, it may be that your horse feels bad with SBM because he is getting a glucose hit. In his case, adding SBM won’t work until the IR is under control. Many horses achieve this with just the removal of grain but there are others that due to reasons such as a different microbiome, just don’t get the same results. Remember that in mice it has been shown that the microbiome of thin mice placed into fat mice cause weight reduction while on the same diet. With a relatively high glucose diet in some horses like yours, maybe there won’t be a reduction in body fat / IR until the gut microbiome is changed. My hypothesis is that through glucose restriction and exercise, this might occur.

Remember that aerobic exercise means that the body uses fat for the fuel, not glucose. If there is little glucose in the diet then this exercise will burn off the body fat as well as starve the glucose dependent gut microbes. But if the glucose is still high in the diet then the lost body fat will be replaced with insulin dependent conversion of new glucose into body fat for a net even exchange or increase. And the gut microbiome won’t change.

Decrease glucose intake and increase exercise. Until you do this you have not ruled out this as the cause of his lethargy. Personally I think this makes more sense than to call it an “allergy.” As far as the corneal ulcers goes, could these ulcers have the same cause as gut ulcers (gastric, colonic, etc)? The primary reason for all gut ulcers in humans has been shown to be an altered gut microbiome. There is a “holomicrobiome” that describes the bacteria that live in, on and around us. They are the “good guys.” If the corneal ulcers are reduced or eliminated after decreasing the glucose intake and increasing the exercise then we ALL want to know this.

One more point – start the exercise slowly. Lounging for 45 minutes is not good for a horse even in great athletic shape. It might be better to pony them without a rider’s weight at first. Walking them in hand for a bit will increase your exercise as well but I understand all of this takes time and there is harsh weather for many. Restricting glucose is the best option with add exercise when you can do it. Remember to make a journal of all of this (notes on a calendar). Report back when you have some results! Doc T

[Doc-t]

Sorry for the delay but for some reason this was marked as spam!!! One more gremlin to fix!

Then I wrote a very long answer to this and now it has disappeared! Yikes! This is an EXCELLENT reason to write first in a tex editor and then paste it here. I have no backup now so I need to re-write it.

I’ll get to it again but I think you will discover there is another possibility…. hang on. I want to post this first to make sure replies are working.